An Orthogonal Frequency Division Multiplexing (OFDM) technology can dynamically allocate a bit sequence of high-speed serial service data to subcarriers whose spectrums are mutually overlapping and orthogonal, and is extensively studied and applied increasingly in the field of optical communications.
In the field of optical communications, a traditional practice is that, after an OFDM analog electrical signal is generated, the OFDM analog electrical signal is modulated by using in phase quadrature phase-shift keying Mach Zehnder (IQMZ) modulator to obtain a signal sideband OFDM optical signal. When the OFDM analog electrical signal is generated, from the perspective of the frequency domain, service data is only filled in a positive sideband, and no service data is filled in a negative sideband: That the length of FFT/IFFT is 1024 is used as an example. 1024 subcarriers can be filled in the entire frequency band, where the first to the 512th subcarriers belong to a positive sideband, and the 513th to the 1024th subcarriers belong to a negative sideband. Service data is only filled in the second to the 512th subcarriers, a direct current component is filled (for example, 0 is filled) in the first subcarrier, and 0 is filled in the 513th to the 1024th subcarriers.
Because service data is only filled in the positive sideband, and no service data is filled in the negative sideband, the negative sideband is not utilized, and bandwidth utilization needs to be improved.